As is commonly known, variable displacement compressors having a swashplate are used in air conditioning systems of motor vehicles. Such compressors typically include at least one piston disposed in a cylinder of a cylinder block and a rotor assembly operatively coupled to a drive shaft. The swashplate is coupled to and adapted to be rotated by the rotor assembly during rotation of the drive shaft. The swashplate is variably angled relative to the drive shaft between a minimum angle of inclination and a maximum angle of inclination. Each piston slidably engages with the swashplate through a shoe as the swash plate rotates, thereby causing each piston to reciprocate within the corresponding cylinder of the cylinder block. As the angle of inclination of the swashplate is varied, so too is the displacement of each piston within each cylinder, thereby causing the flow rate of a refrigerant flowing through the compressor to vary. The flow rate varies between a maximum flow rate when the swashplate is positioned at a maximum angle of inclination relative to the drive shaft and a minimum flow rate when the swashplate is positioned at a minimum angle of inclination relative to the drive shaft.
It is not uncommon for variable displacement compressors to develop suction pulsations. The suction pressure pulsations may propagate throughout the air conditioning system. When these pressure pulsations reach certain components of the air conditioning system, such as the evaporator, the pressure pulsations may cause noise to be generated that can be heard in a passenger compartment of the vehicle.
The problem of noise generation caused by suction pulsation has previously been addressed by the addition of a suction damping device within the variable displacement compressor. The suction damping device traditionally includes a spring loaded plunger reciprocatingly disposed within a body having flow openings formed therein. The position of the plunger within the body determines a cross-sectional flow area by which the refrigerant may flow through the suction damping device during different operating modes of the variable displacement compressor.
There are two primary methods for determining the position of the plunger of the suction damping device and therefore the flow rate of the refrigerant through the suction damping device. One method includes the flow of the refrigerant entering the compressor exerting pressure on the plunger to apply a force against the biasing of the spring in contact with the plunger. The depression of the spring and subsequent repositioning of the plunger alters the cross-sectional flow area past the plunger to regulate the flow rate of the refrigerant entering the compressor. One issue present when employing this method is that the plunger typically has to be biased by a relatively stiff spring to properly control the pressure pulsations. The use of a stiff spring negatively affects the efficient operation of the compressor by causing the refrigerant to undergo an undesirably large pressure drop when exerting the pressure force on the plunger to open the suction damping device. The use of a stiff spring may also result in a lower maximum flow capacity of the compressor due to the spring preventing a full opening of the suction damping device under certain operating conditions.
The second known method includes using a known pressure difference between a crankcase chamber having the swash plate disposed therein and a suction chamber disposed downstream of the suction damping device to control a position of the plunger within the body. This approach requires the addition of flow passageways within the variable displacement compressor for communicating the refrigerant at the various different pressure values to the suction damping device in order to control the position of the plunger thereof, thereby increasing the complexity of the variable displacement compressor while also presenting additional fluid passageways in need of suitable sealing means and flow control. Such suction damping devices also utilize a spring for biasing a valve element, which may negatively cause the suction damping device to be subject to the effects of hysteresis of the spring when operating under certain conditions.
It would therefore be desirable to produce a suction damping device that minimizes noise generation in an air conditioning system by providing precise control of a variable flow area of a refrigerant flow as the refrigerant flow enters a suction port of a variable displacement compressor.